For many years fire hydrants of the "dry" barrel type have been constructed with a brass or bronze nozzle inserted into a boss provided on a barrel of the hydrant, the brass or bronze nozzle being permanently retained in the boss by calking with lead or the like. In this respect, the nozzles were provided with four inner locking lugs which were given a fractional turn from slots in the boss of the barrel when installed and then calked in place so that the nozzle could not be blown out with water pressure. The difficulty with this type of nozzle construction resulted when it was necessary to replace the nozzle due to damage of the nozzle or wear of the hose threads on the nozzle from use as it usually required the barrel to be removed and returned to the maintenance shop for the repairs or modification.
More recently hydrants have been constructed with replacement nozzles which could be replaced in situ merely by threading the nozzle out of the boss and replacing the nozzle with another nozzle. This does require a machining operation to the cast iron barrel and nozzle as the boss of the barrel and the nozzle respectively had to have threads interiorly and exteriorly machined thereon. However, this gave the hydrants considerable more utility in that the hydrants could be installed and when the situation occurred when it was necessary to change the hydrant nozzle because of damage to the same or because a community makes a change in size of hose connections, the nozzle could merely be unthreaded from the hydrant barrel and replaced so that effectively there was no interruption of service.
However, this arrangement of replaceable nozzles was not entirely satisfactory in that unauthorized personnel could remove the nozzles and thus the hydrant was not completely foolproof. To obviate this, radial holes were drilled through the barrel boss and into the nozzle and either a blind pin was radially inserted into the aligned holes or the hole in the boss was threaded and a threaded lock pin was inserted into the aligned holes. This arrangement, while functioning to prevent inadvertent removal of the nozzle, has a drawback when it was desired to replace the nozzle since it was difficult to get the holes to align when the nozzle was threaded back onto the hydrant or if a new nozzle was installed it required drilling of the new nozzle at the site of installation.
In prior installations utilizing a replaceable nozzle threaded into a boss into the hydrant barrel, an abutment flange was provided on the nozzle and a sealing ring was inserted between the abutment flange of the nozzle and the outwardly facing surface of the boss. After the nozzle had been inserted into the boss on the barrel at an initial torque, thus loading the sealing ring, in time the sealing ring would cold flow, reducing the gripping effect between the nozzle and the boss, thus making the removal of the nozzle easier and thus reducing the sealing effect of the sealing ring.